MD Settings: Ignore whitespace only search queries.

chrome/browser/resources/settings/settings_ui/settings_ui.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview
  * 'settings-ui' implements the UI for the Settings page.
  *
  * Example:
  *
@@ skipping 143 matching lines @@
 
     this.$.main.searchContents(urlSearchQuery);
   },
 
   /**
    * Handles the 'search-changed' event fired from the toolbar.
    * @param {!Event} e
    * @private
    */
   onSearchChanged_: function(e) {
-    var query = e.detail;
+    // Trim leading whitespace only, to prevent searching for empty string. This
+    // still allows the user to search for 'foo bar', while taking a long pause
+    // after typing 'foo '.
+    var query = e.detail.replace(/^\s+/, '');
+    // Prevent duplicate history entries.
+    if (query == this.lastSearchQuery_)
+      return;
+
     settings.navigateTo(
         settings.Route.BASIC,
         query.length > 0 ?
             new URLSearchParams(`search=${query}`) : undefined);
   },
 
   /**
    * @param {Event} event
    * @private
    */
   onIronActivate_: function(event) {
     if (event.detail.item.id != 'advancedPage')
       this.$$('app-drawer').close();
   },
 
   /** @private */
   onMenuButtonTap_: function() {
     this.$$('app-drawer').toggle();
   },
 
   /** @private */
   directionDelegateChanged_: function() {
     this.$$('app-drawer').align = this.directionDelegate.isRtl() ?
         'right' : 'left';
   },
 });